1. Field of the Invention
The present invention relates generally to particle fuel burning furnaces and, more particularly, is concerned with a device mounted across the upper combustion chamber of the furnace which controls filling of the upper chamber with particle fuel by detecting the height of the pile of particle fuel contained therein.
2. Description of the Prior Art
In times of constantly increasing energy costs, the utilization of waste materials as fuel to produce energy is of increasing importance. Waste materials are amply available from various sources, for example, agricultural, forestry and industrial operations.
Many different furnaces (including incinerators and the like) appear in the prior art for burning conventional types of fuel, such as coal and wood, as well as waste or by-product types of particle fuel, such as sawdust, pulverized trash and wood chips. Representative of the prior art are the furnaces disclosed in U.S. patents to Barnett (No. 2,058,945), Evans (No. 3,295,083), Midkiff (No. 3,822,657), Kolze et al (Nos. 3,865,053; 4,311,102; 4,377,115), Culpepper, Jr. (Nos. 3,932,137), Leggett et at (No. 3,951,082), Probsteder (No. 4,218,980), Payne et al (No. 4,378,208), Voss (No. 4,385,567) and Ekenberg (No. 4,430,949).
Another prior art furnace for burning waste product particle fuel is manufactured by Eshland Enterprises, Inc. of Greencastle, Pa. under the trademark "Wood Gun". Generally referred to as a wood gasification boiler, it has an insulated housing in which an upper, primary particle fuel retention and combustion chamber and a lower, secondary or afterburning combustion chamber are formed by refractory materials. A series of generally vertically extending passageways interconnect the bottom of the upper chamber with the top of the lower chamber. A quantity of waste particle fuel delivered into the upper chamber of the boiler through a fuel inlet in the top of the housing falls toward the bottom of the upper chamber and forms into a pile of fuel particles. The pile of particle fuel is ignited and burns from the bottom adjacent the location of the passageways. Periodically, the pile is replenished by delivery of additional particle fuel through the top fuel inlet of the housing.
Combustible gases generated as by-products from the burning of the particle fuel in the upper, primary chamber, along with air introduced into the upper portion of the primary chamber above the pile of fuel, are drawn downward through the passageways into the lower, secondary chamber by a draft inducing fan which creates a negative pressure drop in the lower chamber relative to the upper chamber. A suitable heat recovery unit is connected to the lower combustion chamber for capturing much of the heat produced by burning the combustible gases therein.
The above-described boiler has proven to be an efficient and economical way to convert waste products into usable heat energy. For the most part, the overall performance of the Eshland WOOD GUN wood gasification boiler has met and even surpassed expectations since its introduction. However, from time to time in any product, and the Eshland boiler is no exception, a need arises to make certain improvements which will solve problems which crop up and increase performance and productivity even further.